05 Classification of.. - Department of Earth and Planetary Sciences

106
Classification of Meteorites
Figure 17
Bulk oxygen isotopic compositions of primitive achondrites and differentiated meteorites (sources
Clayton and Mayeda, 1996; Yamaguchi et al., 2002).
EET84302 is texturally and mineralogically
intermediate between acapulcoites and lodranites
(Takeda et al., 1994; Mittlefehldt et al., 1996;
McCoy et al., 1997a,b).
LEW86220 is related to acapulcoites and
lodranites through both its oxygen isotopic
(Figure 17) and mineral compositions (Clayton
and Mayeda, 1996; McCoy et al., 1997b). This
meteorite contains two lithologies: one is coarse
grained and has mineralogy similar to acapulcoites,
and the other is very coarse grained (up to 9 mm)
and consists of FeNi-metal, troilite, plagioclase,
and augite (Mittlefehldt et al.,1998).
Cosmic-ray exposure ages are between
,5.5 Ma and 7 Ma for all acapulcoites and most
of the lodranites, possibly indicating sampling
from a single impact event on a common parent
body (McCoy et al., 1996, 1997a,b).
1.05.4.1.2 Winonaites and the
silicate-bearing IAB
and IIICD irons
Winonaites have roughly chondritic mineralogy
and chemical composition (Table 6), but
achondritic, recrystallized textures (Figures 16(c)
and (d)). They are fine- to medium grained,
mostly equigranular rocks but some (Pontlyfni
and Mount Morris (Wisconsin)) contain what
appear to be relic chondrules. Their mineral
compositions are intermediate between those of
enstatite and H chondrites, and FeNi–FeS
veins that constitute the first partial melts of
a chondritic precursor material are common
(Benedix et al., 1998).
Silicate inclusions in IAB irons are linked
through oxygen isotopic (Figure 17) and mineral